Re: task server

[Bas Wijnen]

Marcus Brinkmann wrote:
> There is something that needs to be said about task death
> notifications.  Notifications in L4 are an impossibility for us.  It's
> simply not possible to implement them robustly and securely.
> Everywhere where we are saying notifications, we actually mean some
> sort of polling mechanism (a dedicated thread in the client polling
> for new events).

Actually, if it's a dedicated thread, then it should be possible:
1 - A calls an IPC to task, with infinite receive timeout.
2 - task notes that A is ready to receive a message.
3 - A sends (from a different thread) a notice to task that it wants to 
be notified when B dies.
4 - Task records this.
5 - same for C.
6 - Task records this.
7 - B dies.
8 - Task sends a message about it to A.
9 - C dies.
10- Task waits (and does _not_ notify A yet.)
11- A has handled the death of B and starts receiving again (using the 
same system as in 1.)
12- Task sends a message about C's death to A.
etc.

If task's death notification fails, then the receiving task is not 
behaving correctly, and may not expect anything (it may not receive any 
notifications anymore, it will definately not receive the same death 
notification again, it may be killed by task, anything can happen.)

Thanks,
Bas

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